# std::strstreambuf

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< cpp‎ | io

Defined in header `<strstream>` |  |
class strstreambuf : public std::basic_streambuf<char> |  | (deprecated in C++98) (removed in C++26)

`std::strstreambuf` is a std::basic_streambuf whose associated character sequence is a character array, which may be constant (e.g. a string literal), modifiable but not dynamic (e.g. a stack-allocated array), or dynamic, in which case the `std::strstreambuf` may be allowed to reallocate the array as necessary to accommodate output (e.g. by calling delete[] and new[] or user-provided functions).

Typical implementation of a `std::strstreambuf` holds four private data members:

1) buffer state, a bitmask type which can represent any combination of the four values "allocated" (destructor will deallocate), "constant" (output not allowed), "dynamic" (output may reallocate), or "frozen" (deallocation and reallocation are not allowed)
2) allocated buffer size (the beginning of the buffer does not need a special data member, it may be stored in the inherited pointer eback())
3) pointer to user-provided allocation function
4) pointer to user-provided deallocation function.

### Notes

After any call to str() on a stream with a dynamic buffer, a call to freeze(false) is required to allow the `strstreambuf` destructor to deallocate the buffer when necessary.

`strstreambuf` has been deprecated since C++98 and removed since C++26. The recommended replacement is `std::spanbuf`(since C++23).

### Member functions

### Public member functions
(constructor) | constructs a `strstreambuf` object (public member function)
(destructor) [virtual] | destructs a `strstreambuf` object, optionally deallocating the character array (virtual public member function)
freeze | sets/clears the frozen state of the buffer (public member function)
str | marks the buffer frozen and returns the beginning pointer of the input sequence (public member function)
pcount | returns the next pointer minus the beginning pointer in the output sequence: the number of characters written (public member function)
### Protected member functions
underflow [virtual] | reads a character from the input sequence without advancing the next pointer (virtual protected member function)
pbackfail [virtual] | backs out the input sequence to unget a character (virtual protected member function)
overflow [virtual] | appends a character to the output sequence, may reallocate or initially allocate the buffer if dynamic and not frozen (virtual protected member function)
setbuf [virtual] | attempts to replace the controlled character sequence with an array (virtual protected member function)
seekoff [virtual] | repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function)
seekpos [virtual] | repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function)

## Inherited from std::basic_streambuf

### Member types

Member type | Definition
`char_type` | `CharT`
`traits_type` | `Traits`; the program is ill-formed if `Traits::char_type` is not `CharT`.
`int_type` | `Traits::int_type`
`pos_type` | `Traits::pos_type`
`off_type` | `Traits::off_type`

### Member functions

(destructor) [virtual] | destructs the `basic_streambuf` object (virtual public member function of `std::basic_streambuf<CharT,Traits>`)
##### Locales
pubimbue | changes the associated locale and invokes imbue() (public member function of `std::basic_streambuf<CharT,Traits>`)
getloc | obtains a copy of the associated locale (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Positioning
pubsetbuf | invokes setbuf() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekoff | invokes seekoff() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekpos | invokes seekpos() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubsync | invokes sync() (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Get area
in_avail | obtains the number of characters immediately available in the get area (public member function of `std::basic_streambuf<CharT,Traits>`)
snextc | advances the input sequence, then reads one character without advancing again (public member function of `std::basic_streambuf<CharT,Traits>`)
sbumpcstossc (removed in C++17) | reads one character from the input sequence and advances the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sgetc | reads one character from the input sequence without advancing the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sgetn | invokes xsgetn() (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Put area
sputc | writes one character to the put area and advances the next pointer (public member function of `std::basic_streambuf<CharT,Traits>`)
sputn | invokes xsputn() (public member function of `std::basic_streambuf<CharT,Traits>`)
##### Putback
sputbackc | puts one character back in the input sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sungetc | moves the next pointer in the input sequence back by one (public member function of `std::basic_streambuf<CharT,Traits>`)

### Protected member functions

(constructor) | constructs a `basic_streambuf` object (protected member function)
operator= (C++11) | replaces a `basic_streambuf` object (protected member function)
swap (C++11) | swaps two `basic_streambuf` objects (protected member function)
##### Locales
imbue [virtual] | reacts to a change of the associated locale (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
##### Positioning
setbuf [virtual] | replaces the buffer with user-defined array, if permitted (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
seekoff [virtual] | repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
seekpos [virtual] | repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
sync [virtual] | synchronizes the buffers with the associated character sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
##### Get area
showmanyc [virtual] | obtains the number of characters available for input in the associated input sequence, if known (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
underflow [virtual] | reads characters from the associated input sequence to the get area (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
uflow [virtual] | reads characters from the associated input sequence to the get area and advances the next pointer (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
xsgetn [virtual] | reads multiple characters from the input sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
ebackgptregptr | returns a pointer to the beginning, current character and the end of the get area (protected member function)
gbump | advances the next pointer in the input sequence (protected member function)
setg | repositions the beginning, next, and end pointers of the input sequence (protected member function)
##### Put area
xsputn [virtual] | writes multiple characters to the output sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
overflow [virtual] | writes characters to the associated output sequence from the put area (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
pbasepptrepptr | returns a pointer to the beginning, current character and the end of the put area (protected member function)
pbump | advances the next pointer of the output sequence (protected member function)
setp | repositions the beginning, next, and end pointers of the output sequence (protected member function)
##### Putback
pbackfail [virtual] | puts a character back into the input sequence, possibly modifying the input sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)

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